It is well known in the subterranean well drilling and completion art that it may be desirable to perform a formation fracturing and propping operation to increase the permeability of the formation adjacent to the wellbore. According to conventional practice, a fracture fluid such as water, oil/water emulsion or gelled water is pumped into the formation with sufficient volume and pressure to create and open hydraulic fractures in the production interval. The fracture fluid may carry a suitable propping agent, such as sand, gravel or proppants into the fractures for the purpose of holding the fractures open following the fracture stimulation operation.
The fracture fluid must be forced into the formation at a flow rate great enough to fracture the formation allowing the entrained proppant to enter the fractures and prop the formation structures apart, producing channels which will create highly conductive paths reaching out into the production interval, and thereby increasing the reservoir permeability in the fracture region. As such, the success of the fracture stimulation operation is dependent upon the ability to inject large volumes of fracture fluids into the formation at a pressure above the fracture gradient of the formation and at a high flow rate.
It has been found, however, that following a fracture stimulation operation, the large volume of fracture fluids pumped into the formation migrates back to the well resulting in substantial fluid accumulation. In relatively low pressure or pressure depleted gas producing wells this may present a particular problem. Specifically, the reservoir pressure in some cases is not high enough to unload the fluid from the well. This results in a substantial decrease in the volume of gas production or worse, the hydrostatic pressure of the fluid column completely prevents gas production.
Similarly, as a gas well ages, water encroachment may occur. In a healthy, optimally producing well, high pressure gas flow has the ability to lift this liquid to the surface. Over time, however, as the gas pressures in the formation declines and water production increases, the flow conditions change. The reservoir pressure may no longer be sufficient to unload the well such that water accumulates in the lower section of the well forming a column which further retards gas production. In fact, as the column height increases, the hydrostatic pressure may completely prevent gas production.
Several solutions have been suggested to overcome the fluid accumulation problem and to restore the flow rate of gas producing wells. Two such solutions are jetting and swabbing the well. In jetting, a low density fluid such as a nitrogen is pumped downhole via a coiled tubing unit to lighten the offending liquid column such that the liquid can be lifted to the surface. In swabbing, a swab is operated, for example, on a wireline, to bring fluids to the surface and return the well to a state of natural flow.
The existing solutions, however, are beset with numerous limitations. Jetting and swabbing both require a rig crew to rig up the required equipment, perform the jetting or swabbing operation, then dismantle the equipment after performing the operation. A substantial amount of time and money are associated with rigging up and rigging down. In addition, no gas stream may be produced during these operations. Moreover, with jetting and swabbing, as with any downhole operation that involves killing the well, there is a risk that the well will not come back on line. Furthermore, if the well comes back on line, additional fracture fluids or water may enter the well requiring subsequent jetting or swabbing operations.
Therefore, a need has arisen for a system and method for overcoming the fluid accumulation associated with fracture stimulation treatments and the aging of gas wells. A need has also arisen for such a system and method that restore the flow rate of the gas producing well after fluid accumulation. Further, a need has arisen for such a system and method that do not require mobilizing a rig crew and killing the well to remove fluid accumulation.